YSI 550A-100 Dissolved Oxygen Meter (Electrochemical Polarographic Type)

Overview

The YSI 550A-100 Dissolved Oxygen Meter is a rugged, field-deployable electrochemical instrument engineered for high-reliability measurement of dissolved oxygen (DO) and temperature in freshwater, seawater, and wastewater environments. It employs a Clark-type polarographic sensor principle—where oxygen diffuses through a selective polyethylene (PE) membrane onto a cathode surface, generating a diffusion-limited current proportional to the partial pressure of dissolved O₂. This well-established electrochemical method ensures stable, traceable measurements aligned with standard methods including ASTM D888 and ISO 5814. The instrument integrates YSI’s proprietary thermistor-based temperature sensing—recognized globally for its precision and long-term stability—to enable automatic temperature compensation and salinity correction (0–70 ppt). Designed for both laboratory bench use and extended field campaigns, the 550A-100 features full IP67 ingress protection, shock-resistant housing, and an integrated probe storage/calibration chamber that maintains electrode hydration and readiness between measurements.

Key Features

• IP67-rated waterproof and impact-resistant enclosure suitable for immersion, rain exposure, and transport without protective cases
• Field-replaceable polarographic DO probe module—no tools required; enables rapid sensor maintenance without instrument downtime
• Next-generation PE membrane technology delivering <9-second t₉₅ response time and significantly reduced stirring dependence compared to conventional Teflon membranes
• Stainless steel probe body with optimized hydrodynamic profile for easy submersion and minimal flow disturbance
• Strain-relief fittings at both cable termini to mitigate mechanical fatigue and extend service life of 30-meter cable (standard on 550A-100)
• Onboard calibration chamber doubles as probe storage—maintains electrolyte hydration and prevents membrane drying during transit or idle periods
• High-contrast LCD with dual-parameter display (DO in mg/L and % saturation, plus temperature in °C) and configurable resolution (0.01 or 0.1 mg/L; 0.1 or 1% saturation)

Sample Compatibility & Compliance

The YSI 550A-100 is validated for use across diverse aqueous matrices: potable water, surface runoff, estuarine and marine systems (up to 70 ppt salinity), activated sludge, and industrial effluents. Its polarographic sensor design minimizes interference from sulfides, chlorine residuals, and moderate levels of hydrogen sulfide—common challenges in wastewater monitoring. The instrument complies with key regulatory frameworks governing environmental data integrity, including EPA Method 360.1 (for DO in natural waters) and supports GLP-aligned workflows via documented calibration logs and user-defined calibration intervals. While not inherently 21 CFR Part 11 compliant (as it lacks electronic signature functionality), its analog output and stable calibration history support audit-ready reporting when used within validated laboratory SOPs.

Software & Data Management

Data acquisition is performed via direct readout and manual logging; the 550A-100 does not feature internal memory or USB/Bluetooth connectivity. However, its analog voltage output (0–5 V DC, scalable to DO range) permits integration with external data loggers, SCADA systems, or programmable logic controllers (PLCs) for continuous monitoring applications. Calibration records—including date, zero-point and span values, temperature, and salinity settings—are retained in user-maintained field notebooks or LIMS entries. For laboratories requiring digital traceability, YSI recommends pairing the 550A-100 with the YSI EcoWatch™ software suite (via compatible interface adapters) to generate PDF reports compliant with ISO/IEC 17025 documentation requirements.

Applications

• Regulatory compliance monitoring under NPDES permits and Clean Water Act reporting protocols
• Biochemical oxygen demand (BOD) incubation studies requiring precise initial and final DO readings
• Aquaculture system management—real-time DO tracking in recirculating aquaculture systems (RAS) and hatchery tanks
• Wastewater treatment plant process control—activated sludge basin profiling, aeration basin optimization, and effluent verification
• Limnological and oceanographic field surveys where portability, battery longevity (>2000 h), and cable reach (30 m) are operationally critical
• Educational laboratory instruction in environmental chemistry and aquatic ecology courses

FAQ

What calibration standards are required for the YSI 550A-100?

Zero calibration uses sodium sulfite solution (0 mg/L DO); span calibration uses air-saturated water (temperature- and pressure-dependent) or certified DO standard solutions (e.g., Winkler-titrated reference samples).
Can the 550A-100 measure DO in high-turbidity or viscous samples?

Yes—the stainless steel probe and low-stirring-dependence PE membrane allow reliable operation in suspended solids up to 1000 mg/L and moderately viscous media such as activated sludge; however, membrane fouling requires more frequent cleaning.
Is temperature compensation automatic?

Yes—integrated thermistor continuously measures sample temperature and applies Nernst-based compensation in real time; salinity input (0–70 ppt) is manually entered prior to measurement.
How often should the DO membrane and electrolyte be replaced?

YSI recommends replacing the PE membrane and filling electrolyte every 2–4 weeks under continuous use, or immediately after exposure to oils, solvents, or heavy biofouling.
Does the 550A-100 meet ISO 5814:2012 requirements?

Its polarographic measurement principle, specified response time (<12 s), and accuracy specifications align with ISO 5814:2012 for Class 2 portable DO meters; formal conformity assessment requires third-party verification per ISO/IEC 17025.